This invention relates to hydraulic bottom-hole motors for drilling wells for the purposes of prospecting for and production of oil, gas and other mineral resources, and more specifically to turbodrills for drilling wells, preferably with the employment of diamond bits.
At present diamond bits are being widely employed, and they are efficient with rotational speeds exceeding the values generally used for rotary bits.
Known in the art is a turbodrill for drilling wells comprising a housing with stators fixed therein having blades forming a circular pattern and defining guide passages for the flow of drilling fluid, which is fed by means of mud pumps, and a shaft mounted in the housing by means of an axial support having rotors fixed thereto, the blades of the rotors forming a circular pattern and being directed oppositely to the stator blades so as to change the direction of flow of drilling fluid, the stator and rotor blades being mounted in a manner such as to form the turbodrill turbine stages in which the linear motion of drilling fluid transformed into the rotary motion of the rotors, and means for fixing the turbine stages to the shaft and housing, respectively.
During the operation of the above-described turbodrill with diamond bits, the shaft rotates at high speeds as compared to those used for conventional turbodrills. Since the rotational speed of turbodrills cannot be controlled, the incidence angle of flow at the blades may vary over a wide range during the drilling to attain its maximum in the zone of extreme operating conditions (breaking or idling). The flow through the blade patterns occurs with the angles of attack which are larger than those inherent in conventional turbodrills thus resulting in considerable energy losses. In practice, this brings about a large growth of the pressure difference in the turbodrill during the braking when using a turbine having slightly cambered blades or during the idling when using a turbine having strongly cambered blades. Such an abrupt change in the pressure difference in a turbodrill causes heavy problems in operation (frequent damages to the protective diaphragms of pumps and the like). In addition, strongly cambered blades have a relatively low efficiency.
When using patterns with axial entrance of the flow and blades with relatively thin inlet edges, the flow is separated from the blade surfaces, and a considerable growth of the pressure difference occurs during the braking, which also makes the operation of a turbodrill difficult. With thickened inlet edges of the blades, this effect is reduced, but in this case, a considerable reduction of the turbodrill efficiency occurs due to increased profile energy losses, thereby impairing the power characteristics, and primarily, the torque value. It is this value that determines the load taken by the turbodrill, that is the opportunity of attaining necessary drilling conditions, with other conditions being equal.
The attempts to use a known turbodrill for diamond drilling were ineffective either due to an abrupt growth of the pressure difference in the delivery line of the pump unit during the braking of the turbodrill shaft, or due to a low efficiency of the motor impairing its torque response.
In known constructions of turbodrills, the thrust bearing can be also used as a seal to limit the leakage of drilling fluid at the turbodrill shaft outlet. Since in this case, the main flow of drilling fluid through the passages of a coupling member or through the passages of the shaft is directed to the central passage of the shaft, a low velocity zone is formed in the space between the shaft and housing, wherein the thrust bearing is accommodated. As a result, the heaviest fractions may be precipitate from the drilling fluid to penetrate into the bearing assembly. The absence of any protection of the turbodrill bearing against penetration of coarse abrasive particles results in premature wear. A failure of the turbodrill support will require premature pulling of the bit out of the hole. In case of using diamond bits, every additional pulling of the bit results in losses of diamonds, whereby the service life of the bit is shortened, thus reducing the efficiency of drilling. For that reason, the problem of increasing the bearing life is of prime importance for turbodrills used with diamond bits.
The disadvantages of known turbodrills also include complicated and unreliable fastening of parts to the shafts.